1. Technical Field
The present invention relates to a method for dividing a wafer into a plurality of chips, and methods for manufacturing silicon devices and liquid ejecting heads using the method for dividing the wafer.
2. Related Art
A liquid ejecting head in which pressure generators such as piezoelectric elements apply pressure to liquid in pressure-generating chambers to eject liquid droplets from nozzle openings is known. A typical example of such a liquid ejecting head is an ink jet recording head that ejects ink droplets. An ink jet recording head that has a channel-forming substrate provided with pressure-generating chambers is known. The channel-forming substrate has pressure generators such as piezoelectric elements provided on one surface, and a nozzle plate having nozzle openings and bonded to the other surface.
Such a channel-forming substrate constituting an ink jet recording head is formed of, for example, a silicon single-crystal substrate. In general, in forming the channel-forming substrate, a plurality of channel-forming substrates are integrally formed in a wafer, such as a silicon wafer, and the wafer is divided into pieces.
JP-A-2002-313754 (pp 4-9, FIGS. 1 and 2) discloses a method for dividing a wafer, in which, for example, a break pattern consisting of a plurality of through-holes aligned at a predetermined interval is provided along a planned dividing line between channel-forming substrates (chips) in a silicon wafer. By applying an external force to the silicon wafer, the silicon wafer can be divided along the break pattern. In a method for manufacturing ink jet recording heads, when a silicon wafer is divided by applying this method, the silicon wafer is divided at fragile portions between the through-holes constituting the break pattern by receiving the external force. As a result, a plurality of channel-forming substrates (chips) can be obtained.
Thus, by providing a break pattern in a silicon wafer, the silicon wafer can be divided into a plurality of channel-forming substrates with relative ease.
However, because it is difficult to divide a silicon wafer (the fragile portions) constantly at a desired position and in a desired shape, the silicon wafer may be divided at a portion other than the fragile portions between the through-holes. Further, the channel-forming substrates as finished products can have cracks originating at corners of the through-holes.
In particular, in the case of manufacturing liquid ejecting heads such as ink jet recording heads, there is a problem in that the fracture surface may produce fine dust, depending on the breakage condition, and the dust may adhere to the inside of the channel, thereby clogging the nozzles or the like. There is another problem in that, in the case of forming a thin film or the like on the channel-forming substrate, the dust may adhere to the surface thereof. This prevents proper formation of the film, and degrades the yield.
Further, in the case of providing fragile portions by irradiation with a laser beam, components provided on the wafer may block the laser beam. To avoid this, the components need to be provided at positions distant from regions to become the fragile portions. This decreases the number of silicon devices obtainable from a wafer and leads to a high manufacturing cost.
In particular, in the case of providing fragile portions in a thick wafer by irradiation with a laser beam, components on the wafer need to be provided at positions distant from the fragile portions, whereby the number of silicon devices obtainable from a wafer is further decreased.
Further, in the case of providing fragile portions in the thickness direction of a wafer by irradiation with a laser beam, processing time becomes long.
In the case of providing fragile portions in a thin wafer, the rigidity of the wafer decreases. This may lead to breakages and cracks, whereby handling of the wafer becomes troublesome.